


Feral Instincts

by ASKR



Category: Fate/Grand Order, Fate/stay night & Related Fandoms
Genre: Blood and Injury, Blood and Violence, Broken Bones, Creampie, Gore, Injury, Knotting, Mild Gore, Other, Please take the tags seriously this is... not a good fun time, Rape, Rape/Non-con Elements, Reader has a vagina, Sexual Violence, Size Kink, Tail Bondage
Language: English
Status: Completed
Published: 2019-03-23
Updated: 2019-03-23
Packaged: 2019-11-27 16:27:03
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Rape/Non-Con
Chapters: 1
Words: 3,051
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18196574
Author URL: https://archiveofourown.org/users/ASKR/pseuds/ASKR
Summary: Losing all three Command Seals doesn't necessarily mean you can't be Master to your Servant anymore, a pact is a pact after all.However, the Berserker class is a particularly volatile Servant to have, and when Cu Chulainn (Alter) has an urge he himself isn't particularly familiar with like he is with the urge to kill, you might learn first hand what the Mad King is capable of.





	Feral Instincts

Drops of blood created tiny, barely audible splashes as they drip rhythmically from Gae Bolg’s shaft.

Although his Master was no longer in sight, Cu could still hear their shoes as they hit the ground with each hurried step, sprinting away from him.

The fear he’d seen was unmistakable. He could surmise it had something to do with the fact that his Master had used their last Command Seal after having been ambushed alone and needing immediate help, effectively leaving them with no means to control the Mad King any longer.

Instantly upon being teleported to their aid only a few minutes prior, Cu had immediately dispatched the threat - a group of mages. Only their viscera remained now within the room, their blood coating the walls, floor, and dripping from Cu’s own body.

And then with the silence of death heavy in the air, he’d turned to his Master and suddenly the urge to _keep_ _going_ overwhelmed him, a hunger forming a knot below his navel. Cu remained still, not particularly in a hurry to pursue his Master despite the urge gnawing at him to give chase.

Though he never had any intention of killing his Master, preferring to continue to fight their Grail War - Command Seals or not - his sudden urge to give chase filled his chest with an excitement he couldn’t parse.

Darting his tongue across his lips, Cu grinned. Perhaps then, this was what it meant to want to chase for the thrill itself, as opposed to hunting exclusively with the goal of killing.

The memory of his Master’s fearful expression before turning tail and taking flight filled him with an unfamiliar - but enjoyable - anticipation, and Berserker took off into a sprint in the direction of distant footsteps.

 

* * *

 

Your chest burns as you brace yourself against the wall, hunched over trying to catch your breath and maybe some of your bearings.

Glancing around, you try to take in your surroundings to get an idea of where you are within the old, maze-like decrepit mansion you’d been trying to get out of. But nothing stands out as familiar from when you first came in.

Having cut off your supply of mana to your servant, you were hoping Cu wouldn’t be able to find you before running out of what he had left; that perhaps in his madness he wouldn’t think to conserve.

Removing your forearm from the wall, you turn and place your back flush against it, deciding it wouldn’t be any use running until exhaustion leaves you incapacitated.  
Closing your eyes, you concentrated carefully on the sounds around you - your own breathing, the sound of your clothing shifting along with you when you moved even the slightest bit, an occasional drip off in the distance.

You spend minutes almost perfectly still in silence, trying to hear even the slightest bit of movement in the darkness, worried that if you aren’t on constant high alert you’ll miss an opportunity to defend yourself or escape.

A sudden chill of fear that ripples down your spine and through every nerve prompts you to open your eyes.

The sight before you makes your stomach drop, threatening to eject its contents as you stand face to face with your servant, his massive body towering over you from only inches away.

The grin spread across his blood-spattered face was unlike anything you’d seen from him throughout your time as his Master, your fear threatening to collapse your knees from beneath you at any moment.

Not wanting to be on the receiving end of Berserker’s madness, instinct pushes your forward and you make a break for it, ready to run for your life and use whatever spells you could to delay Cu.

But you were already too late to have a chance at making it away. You only manage a few steps before Berserker’s thick, spiked tail swings in front of your feet, knocking you off balance.

Before you can even hit the ground, however, the large appendage snares around your waist tightly, lifting you into the air and swinging you backwards with little effort, slamming your body against the wall. You let out a strangled cry at the force of the impact against your back, blunt pain throbbing across your shoulders.

“Berserker,” you choke out, reaching down to try and push the tail snaked snugly around your waist away. He responds to your actions by squeezing it around you more tightly. Each movement from either of you threatens the pointed spikes on his tail to pierce your skin, but still you place your hands against it and try to push yourself free from the increasingly constricting grip.

The rough, abrasive surface of Cu’s tail alone is enough to deter you from trying for too long to pry yourself free, the harsh tissue scraping away at the skin of your palm painfully.

“We can still win the Grail as a team together,” you plead with desperation, the pressure of being squeezed making you force out each strained word, “you want it still, don’t you?”

Looking away from where your bloodied hands push at his tail, you meet his gaze to plead your case, but Cu simply looks down at you with a scowl.

“Stop squirming or I’ll rip your head off,” he growls.

The words leave you paralyzed in place, your mouth slightly open in surprise as you don’t even dare to move again, only watching him like an animal cornered by its predator.

You flinch when he suddenly moves the hand grasping Gae Bolg, expecting no less than to be eviscerated by Berserker’s weapon; however he simply tossed it to the side - the weapon reverberating as it bounced off the ground and rolled away.

It strikes you then that you’re still alive; and given your experience around Berserker, that itself meant a lot. He’d never taken his time like this with any of the mages and servants alike he’d fought - and made it explicitly clear that no-bullshit killing was his expertise.

“A-” Cu reacts swiftly and cuts you off with a hand over your mouth, the pressure forcing your head back to be strike against the wall, leaving you dazed.

Watching him with a heavy lidded gaze as your head spins, your arms drop limply to your sides as you accept defeat, leaving your fate entirely in the hands of a madman; one that seems particularly unhinged.

Removing his hand from your mouth, Berserker grabs you by the thigh and holds your thigh to his waist so that he can slide himself between your legs until his body is pressed against yours. With his tail holding you firmly in place, he has enough freedom to explore your body with his hands.

Digging his claws in at your thigh and dragging them down, he tears your clothing and the flesh beneath it, the corner of his mouth twitching into a grin as you cry out in pain and try to pull your leg away from his hold - only for the motion to help him along in leaving your pants torn up.

It isn’t until he places a hand to your chest and rips your shirt that it really clicks what Cu was trying to do - you’d assumed there was no goal or method in Berserker’s actions but his claws tearing away at your clothes spell out a clear message of what he wants.

He ravages your clothing to pieces, a deep growl of annoyance rumbling from his chest. Berserker leaves only scraps of fabric to fall to the ground while some remained hanging from your body useless for any sort of coverage; exposing your naked body to him.

Without clothes to protect your skin from his abrasive tail, any movement from either of you is painful, the slightest bit of friction enough to scrape away a thin layer of your skin, blood leaking out from beneath his tail.

Berserker places a hand between your bodies to tear away at the clothing above his pelvis without regard for at least keeping his own clothing in one piece, exposing his groin.

You _want_ to look away but can’t bring yourself to do so, trying instead to only glance from the periphery of your vision so that Berserker doesn’t notice you staring as you try to at least get a look at what you’re going to have to deal with.

Chitinous-like armor covered his pelvic area, making clothing seem redundant. Protruding from a slit in the armored plating was his cock; not at all resembling anything human but unmistakably one.

Although the shaft is humanly average in length, it had the same chitin-like dark blue plating as his body along the length of it. Beneath that, the more fleshy part of his dick was bright red. What you can only assume is precum - a lot of it - oozes from the slit, his hand coming down to grasp the head and stroke down, coating the rest of his length with the viscous substance. As he inches closer and begins to stroke himself against your slit, you can’t help but think from a size perspective, it wasn’t so bad.

You tense at the sensation of his cock grinding slowly against you, the tip brushing against your clit with each rock of his hips and leaving a generous coating of whatever warm secretion it was that leaked from the slit of his head.

Though you try to keep still, wanting above all not to endure any further injury, the steady rock from Cu is enough that his tail shifts along with the motion and harshly rubs against your already raw, torn flesh. You bite your lip, trying not to cry out from the sting, but a few choked sobs force their way out.

Having been so wrapped up in enduring the pain, it’s only when you take a moment to glance down that you realize that his cock is much bigger than when you had previously had a look. Now a few more inches longer - you can only estimate the length of your forearm - the circumference tapers significantly thicker going down the shaft, especially at the apparent swollen, bulbous part just below mid-shaft; you can only hope he’s now standing fully unsheathed.

“I-,” you croak hoarsely, “t-that’s not going to fit anywhere.”

Berserker growls irritably, hand jerking slowly at his cock - which could easily be held within both of his palms and still not be fully covered. Enough time passes that you’re sure he’s unsurprisingly opted to ignore what you had to say.

Cu pulls away slightly to give himself space to look down at you, using a thumb to smear around the probably-not-precum he’d secreted all over your hole, the tip of his digit prodding just barely into you. You shudder, feeling particularly sensitive to the slightest bit of contact as he - surprisingly gently - scoops the slime dripping from your folds and pushes it to your entrance.

Without any of the previous gentleness or concern he’d at least shown you when he prepared your cunt, Cu effortlessly lifts you from the wall with his tail. Your mouth drops open and you let out a wail of pain as you feel his tail tear away at your skin, trying in your desperation to at least hold onto it to minimize movement between it and your body.  
Berserker pays little mind to your pain as he lowers you to the ground, releasing your body from his tail’s grip a few inches from the ground - dropping you painfully onto the floor - and pulling away the appendage completely; exposing your torn, bloody flesh to the cool stinging air.

You don’t even bother to move while you’re free from the constrictive hold of his tail, keeping still as your body throbs in a raw pain all over and you try to choke back sobs.

“We’re a team, we can make it fit,” Berserker finally responds to your concern he’d previously ignored as he lowers himself to a squat above you, casually grabbing both of your legs by the thighs and pushing them back toward your chest. He positions his cock to your entrance, red eyes glaring down at you but his lips pulled back in a wolfish grin, “maybe if my Master hadn’t cut off my mana supply I wouldn’t need an alternative.”

Cu’s tail slides carefully beneath your lower half, helping him to keep your ass propped up ‘comfortably’ in the air while your upper back remained flush to the ground. With you positioned where he wants you, Berserker angles the tip of his massive cock at your entrance, poking at the hole a couple of times until he gets the right slant and slides in.

The way his cock is tapered offers some initial ease to his insertion, but all that goes out the window when he sharply shoves his hips forward and plants himself as deeply as your cunt can accommodate. You clench your jaw tightly, muffling a scream from the rough intrusion that stretches you completely to accommodate him. The heavy volume of slimy secretions from him do little to mitigate the pain, and he’s predictable enough that he doesn’t give you any chance to adjust before he’s fucking you with almost the entire length of his beastly dick.

Tears sting at your eyes, rolling from the corners freely. You move a hand to your mouth, stifling your whimpers and cries by biting into your fist. Occasionally, you glance over to Cu, and every time he’s staring you down with a predatory grin while he fucks you into a wrecked, sobbing mess.

The same slimy warmth he’d used to lubricate you leaks into you, the sensation warm and tingly and surprisingly it dulls the pain of being torn apart, replacing it with a pleasure that feels sickening.

Releasing your legs, Cu’s hands instead find your hips, fingers digging into your flesh harshly as he uses the new grip to angle himself deeper - if that were even possible - slamming you against him hard enough that the skin to skin contact claps together loudly in the room.

“Master,” he speaks in a deep, monstrous growl gripped with madness, his ragged breaths and increasingly erratic movements culminating in what seems like a transformation from madman to beast.

It sneaks up on you when suddenly your hips lurch upward and the sensation of a climax washes over you, the vicious fucking practically forcibly dragging an orgasm out of you. You move your hand from your mouth and whimper out a series of hiccoughing gasps, the contractions of your inner walls around his cock dragging out the sick mix of pain and pleasure in a prolonged release that leaves your shaking as you’re forced to ride it out.

It seems as if that’s enough to push Cu into a frenzy. Though your ears are ringing you can make out his repeated growls of ‘Master’ while he fucks into you with feral zeal, the pressure of his grip at your thighs unbearable enough you squirm to try and free yourself.

A sudden loud crack rings deafeningly though the room, followed within an instant by pain beneath his hand on your right hip.

And then you scream.

Cu sheathes himself completely, holding you in place and forcing you to endure as a sudden flood of heat fills your cunt, his cock throbbing with each pump of his release. You feel yourself stretched near the entrance of your hole, but it’s something your mind doesn’t focus on, instead all you can think about is the pain of a shattered bone directly beneath where Berserker is still gripping you to keep you still.

You only release your breath as you start sobbing, your hands searching for something to grip onto as if holding something until your knuckles are white will help with the agony.

Berserker eventually slowly releases his grip from you, sliding his tail from beneath you and lowering your bottom half slowly to the ground.

He shifts from the squatting position down onto his knees, but doesn’t pull out of you. Vaguely you process that he’s stuck tied to you by the base of his cock where his knot swelled upon release. You don’t really care.

Everything Cu does seems like background noise. It’s only when he’s put his massive body over yours, face only inches from you, that his existence even comes back into focus.

Though your eyes are blurry with tears, Berserker seems to have _most_ of his normal senses returned. He doesn’t seem arrogant, or predatory, his features mostly neutral. He parts his lips, pointed tongue trailing the skin of your cheek and catching your tears as they streamline out of the corner of your eye.

“Endure it, Master,” he drones, his hand wiping the tears on the other side. Cu rolls his hips slightly, his cock still emptying a sickening amount of cum that threatens to spill from around his knot.

His unusually calm demeanor serves to reduce your panic, your eyes catching to meet his red-slitted gaze. Your lips shake and you let out little blubbering hiccups, too afraid to really say anything to him.

“Shut up,” he rolled his eyes and leaned into you, putting his rough chapped lips over yours and silencing the little sounds of pain you’d been making. His razor sharp teeth graze your lip just enough to poke tiny holes in your lips that little beads of blood bubble out of.

His tongue promptly licks away each droplet, and he keeps you mostly quiet with an aggressive, clumsy kiss.

It takes time - all the blood from your scraped away skin is completely dry and crusted - when Cu’s knot shrinks enough to slide out of your used, stretched hole; cum spilling onto the floor and pooling below you.

Berserker’s lips part from yours, and he doesn’t linger any longer, planting his feet back on the ground and putting his arms under your limp, abused body. He hauls you up with ease, every nerve in your limbs screaming to just be left there in your pile of pain until you were able to calm down and use healing magic on yourself. Cu seems to take notice of your resistance to being picked up, simply glaring a warning down at you.

“We have a grail to win, Command Seals or not.”

**Author's Note:**

> For over a month I kept joking to my friends that I wanted Berserker Cu to break my pelvis, and then last week I had a misfortunate accident while tubing on a snow hill and got a pelvis injury so this is my way of coping with that.
> 
> I hope you enjoyed a direct result of my own pain.


End file.
